Currently in the United States and in other industrialized countries of the world a major fleet structure exists for over-the-road hauling of liquid products, such as gasoline, diesel and aviation fuels, and even more important, for the hauling of liquid food products, such as milk. The majority of this tank trailer fleet is fabricated from stainless steel, which is used for both the internal fluid container and the exterior skin, the containers having an intermediate section comprising a metallic structural framework and insulation.
Welding is the primary process used to fabricate stainless steel tanks and, consequently, 304L or 316L stainless steels are normally used because of their low carbon content. Stainless steel alloys are normally of the 18-8 designation, which indicates that they contain eighteen percent chromium and eight percent nickel. The balance of the usual formulation is iron, with a variety of stabilizing agents, such as molybdenum, titanium and carbon "getter" elements, introduced chemically to bind the carbon into the structure of the stainless steel and prevent it from precipitating out in the grain boundaries during heat treatment or welding.
Chromium is the element that provides stainless steel with its non-corrosive properties. There are only three primary sources of chromium in the world. These are Kazakstan in the former Soviet Union, and Zaire and Zimbabwe in Africa. Kazakstan and Zaire have closed their chromium markets for economic and political reasons. This has resulted in a major chromium shortage. As a result, the price of stainless steel has increased greatly over the past few years.
A stainless steel tank is not only very expensive, it is also very heavy, weighing as much as 9,500 pounds when empty.
There have been a few attempts to use composite materials in the manufacture of over-the-road liquid transport containers, particularly for use in transporting corrosive chemicals and hazardous waste. One such container is the TANKCON.TM. Fiberglass DOT-412 Transport, sold by Poly-Coat Systems, Inc., Houston, Tex. Unfortunately, ventures into composite materials, such as this, have resulted in containers that weigh as much as their stainless steel counterparts. A TANKCON.TM. container, for example, having a capacity of 5,400 gallons, weights 13,500 pounds.
The patent literature reflects numerous attempts to use composite structures in the manufacture of food containers. Schmeal et al., U.S. Pat. No. 4,640,853, discloses a carbonated beverage can comprising a thermoplastic core and fiber-adhesive wound layers contiguous to the core. Tronsberg, U.S. Pat. No. 4,040,163, discloses a container made of synthetic resin reinforced by fiber material. Collins et al., U.S. Pat. No. 4,120,418, discloses an insulated container lined with polyurethane foam and wherein a plurality of layers of an epoxy resin formulation and glass-fiber material are applied to the foam.
Other patents disclosing composite containers include Coombes, U.S. Pat. No. 5,465,865; Nichols, U.S. Pat. No. 5,156,268; Voorhies, U.S. Pat. No. 4,930,661; Short, U.S. Pat. No. 4,222,804; Short, U.S. Pat. No. 3,956,816; and Jones et al., U.S. Pat. No. 3,669,299. Huegli, U.S. Pat. No. 4,963,408, discloses a composite laminate comprising a high shear strength, load-bearing matrix disposed between an inner core layer and an outer encapsulating layer. The load-bearing matrix comprises a plurality of layers of load-bearing synthetic filaments. The filaments in each of the layers are arranged in differing angular orientations with respect to the longitudinal axis of the laminate structure.
To the inventors' knowledge, however, no one has heretofore made a generally cylindrical container for over-the-road transportation of liquid food products wherein the container has a cylindrical core, comprising a cellular thermoplastic expanded foam material, encapsulated between layers of resin impregnated materials to form a bonded composite sandwich type construction. The core serves both to provide insulation for the container's contents and to enable the encapsulating layers to provide the necessary structural strength.
It is thus the primary object of the present invention to provide an over-the-road transport container for liquid food products, and wherein the container is made of composite materials and weighs substantially less than comparable stainless steel containers.
It is a further object of the present invention to provide a container as aforesaid that is supportable during transportation only at its forward and rearward ends. The container is thus supported like a stainless steel container during over-the-road transport, being substantially unsupported between its forward and rear ends.